This invention relates to a method of adjusting casting sand, and more particularly to a method and apparatus for determining the optimum compactibility (hereinafter referred to as CB) of the casting sand, and for adjusting the casting sand accordingly.
It is well-known that CB is controlled to adjust casting sand in kneading batches (see, for example, Japanese Patent Publication No. 3-76710). In this method, the CB of casting sand is controlled by adding water, while amounts of additives, such as bentonite, new sand, and fine powder, are kept constant in a batch so as to achieve a given target value of the CB. However, the CB of casting sand, as a target value for the control, has been only empirically set, and there has been no method of determining its optimum CB.
On the one hand, there is a method of adjusting the amounts of additives, such as bentonite, new sand, and fine powder, to adjust casting sand on a long-term basis. In this method, the amounts of additives, such as bentonite, are adjusted by measuring the degree of ventilation, the resisting force, the percentage of active clay, and the percentage of total clay, on an hourly or a daily basis. The purpose of this is to keep constant the properties of the casting sand, such as the particle size distribution and percentage of clay thereof. This is because the casting sand is differently affected by heat when being circulated, including during kneading, molding, casting, demolding, and recovery, depending on the weights, shapes, and ratios of sand to metal, of the cast products, and because the casting sand is carried away with the product or through a dust collector.
However, there has been almost no such long-term adjusting method, wherein the deformation property of a casting mold has been considered. In other words, the deformity of a casting mold results from transportation thereof, casting of molten metal thereinto, or loading of weights thereon. Further, this deformity of the mold affects high-precision or thin-walled cast products, which are now strongly demanded in the industry. However, in a conventional long-term adjusting method for casting sand, these relationships relative to the deformities of a casting mold have not been considered, not to mention that there has been no idea to connect the long-term adjustment of the casting sand to the CB. Thus, heretofore there has been no attempt to optimize the target -value of the CB on a batch basis or long-term basis. By considering such present circumstances this invention was devised to provide a method for determining the optimum CB of casting sand, which is connected to the deformation properties of the casting mold in adjusting the casting sand.